Abstract

Inter-ocular suppression occurs when very different images are presented to each eye. Diplopia ensues if different images are superimposed and perceived. The brain removes this unfavourable viewing experience by suppressing one eye’s input to enable clear single vision. Inter-ocular suppression during visual development occurs in response to sufficiently disparate images caused by strabismus (misalignment of the visual axis) or anisometropia (uncorrected difference in refractive error), and if persistent may result in amblyopia. This is reduced visual sensitivity, usually in one eye, to a range of visual functions that cannot be corrected by refraction. Furthermore, binocular vision is reduced or absent.
Depth and extent of suppression is measured across the central visual field in healthy participants with monocularly blurred vision, healthy participants with monocularly reduced luminance using neutral density (ND) filters, and participants with naturally disrupted binocular vision and/or amblyopia. Suppression of spatial stimuli defined by luminance (L) and luminancemodulated noise (LM) was compared to that measured for stimuli defined by contrast-modulated noise (CM), for which there is no change in mean luminance. For all stimuli suppression depth increased with increased imbalance of binocular input. Suppression was of a similar depth across the visual field with imposed blur and localised central suppression was found with ND filters. Microstrabismics showed central suppression, while strabismic amblyopes showed central in addition to hemifield suppression.
Suppression for all participants was measured to be deeper for CM spatial stimuli than for LM spatial stimuli. This is suggested to be a result of CM stimuli engaging more binocular mechanisms of processing, than LM stimuli, thereby becoming more sensitive to disruptions of binocularity such as those produced in the participants in the present study. CM stimuli are therefore more sensitive to detecting suppression, which is associated with amblyopia.